1. Field of the Invention
The present invention relates to an image forming apparatus having a mechanism for moving a sheet in a direction orthogonal to a conveyance direction in image formation onto a back side of the sheet having an image formed on one side.
2. Description of the Related Art
A conventional image forming apparatus for two-sided printing having a mechanism in which a switchback operation is performed on a sheet having a printed image on one side and the sheet is moved toward a lateral direction to a conveyance direction (which is discussed in Japanese Patent Application Laid-Open No. 2007-62960) is described. As illustrated in FIG. 9, a sheet S picked by a sheet feeding roller 901 is conveyed by a registration roller pair 902. On one side of the sheet S, a toner image is transferred by a transfer roller 903, and the toner image is fixed by a fixing roller 904.
When images are formed on the both sides of the sheet S, after a trailing end of the sheet S conveyed by a discharge reversing roller 905 passes through a point C, the discharge reversing roller 905 rotates in a reverse direction (the rotation direction changes to the opposite direction). Then, the sheet S is moved to a side in the direction orthogonal to the conveyance direction (a width direction of the sheet S) by a skew feed roller 906, and the sheet S comes in contact with a reference guide 910.
In a state where a positional accuracy in the width direction of the sheet S is ensured, the sheet S is conveyed by a re-feed roller 907 to merge with a conveyance path of a first side, and conveyed toward the registration roller pair 902. Then, an image is formed on the back side of the sheet S by the transfer roller 903 and the fixing roller 904, and the sheet S is discharged onto a discharge tray 909 by the discharge reversing roller 905.
With the recent demands for downsizing of an image forming apparatus, a conveyance distance from a discharge reversing roller to a re-feed roller tends to be shortened. Further, since a degree of curves of the curved conveyance paths tends to increase due to downsizing of an image forming apparatus, frictional resistance between a sheet and a conveyance guide also increases. As a result, in some cases, a sheet cannot be moved by a skew-feed roller by a required amount so as to cause the sheet to fit along a reference guide.